In broader historical contexts, Empire Reach is called the Terraform Reach. This is a loose cluster of systems in which many worlds were terraformed for oxygen-water-based life about 35 million years ago. When humans discovered the Terraform Reach, these sculpted worlds were long abandoned and, in various degrees, returning to their natural states.
The first human settlers, the Old Settlers, arrived in small numbers, in single ships and small fleets. They settled the terraformed planets, sometimes making transgenic modifications in themselves to adapt to the less-than-Terran environments. They formed no large, long-lasting interstellar organizations and had a low level of interstellar commerce. Their technical level stayed static or slowly declined.
In Schmidt's universe, the Witches of Karres are among the Old Settlers.
In my universe, the Old Settlers have an Early Psionic level of technology and include the Quishonnes of Pharos.
Several centuries later, the next wave of human settlers arrived, the New Terraformers. These came in large, well-organized fleets, with a higher technical level, specifically drawn by scouts' reports of the Terraform Reach. They were able to settle worlds the Old Settlers could not.
The New Terraformers could not match the feats of the Old Terraformers, but they were able to make repairs: They refreshed the supplies of air and water on light and dry worlds with cometary ices; they shaded heat-trap worlds with dust and stratospheric floats, and stripped out the carbon dioxide. They added carbon dioxide to the air on cold worlds, sometimes by re-starting volcanos, sometimes with cometary ices. They re-seeded the biospheres of withered worlds.
In my universe, the New Terraformers have a Middle Psionic level of technology.
The New Terraformers were an idealistic and enterprising colonial group intent on spreading their parent culture. Their own subculture existed primarily in their ships, stations, and shipyards, and was divided into fleets and subdivided into squadrons. The ruling class was the admiralty, with an upper eschelon of fleet admirals and a more or less honorary grand admiral.
At first, the New Terraformers confined themselves to reconditioning worlds that the Old Settlers had never been able to inhabit. But the fleets competed with one another, and honor and power among the admirals was counted in planets. Eventually, the New Terraformers began working on harsh worlds where the Old Settlers barely hung on and had invited them in. Then invitations were contrived: a New Terraformer admiral required it as a condition for alliance with one local Old Settler authority over another. Finally, worlds were taken simply to keep someone else from taking them, and war between New Terraformers and Old Settlers became common. The New Terraformers generally won, assimilating many Old Settlers, driving the others into less terraformed regions of the planets.
By that time, however, the New Terraformers were a different stock. For generations, they had accepted recruits from the Old Settlers and intermarried with them in the cities that sprang up around their shipyards.
The New Terraformers formed no central government, but did form a loose Alliance, policing interstellar commerce and seldom allowing war between members. The old culture of the fleets waned as people took to living on the planets they had been terraforming for so long.
The last wave of human settlement, a few centuries after the New Terraformers had consolidated their hold, was the Koliot Raiders. These were a semi-nomadic, piratical culture, based in their fleets of battle ships, just as the first New Terraformers were based in their terraforming fleets. The Koliot Raiders came to the Terraform Reach fleeing authorities in other human-settled regions and following rumors of a rich concentration of prey in the Reach.
The Alliance was poorly prepared, at first, and the Raiders took over some worlds completely. But the Raiders were relatively small in numbers, short-sighted, and divided among themselves. The Alliance eventually militarized and destroyed them.
In militarizing, the Alliance transformed itself into the Empire. Planets had to be taken, held, and re-taken from the Koliots by military force over long periods of time; the Alliance spaceforce evolved into an arm of the planetary government. But it was a division of government held in common by all the Alliance planets. It became a combination of war department and ministry of off-planet affairs.
The Alliance spaceforce, moving often from planet to planet, became a nomadic society of its own, reviving the culture of the early New Terraformers and mirroring that of the Koliot Raiders. Officers tended to marry officers of like rank and to bring their children up as de facto spacers. Eventually, a small number of families were supplying almost all of the spaceforce admirals, forming a proto-dynasty.
The proto-dynasty became the First Dynasty and the Alliance became the Empire when Tharis tried to withdraw from the Alliance after a decade without Raider activity anywhere in the Terraform Reach. Spaceforce Grand Admiral Clari (later Clari I) refused to allow the withdrawl and sent in ships and troops to enforce this. Eighteen other planets then attempted secession. Clari retained fifteen of them and, in the midst of these battles, was acclaimed empress by the Terraform Reach Alliance Spaceforce High Command, which renamed itself the Imperial Senate.
Clari spent the rest of her life retrieving planets trying to secede from the new Empire. Her successor and adoptive son, Sast, did the same. But his successor, Norren the Great, began adding planets to the Empire – planets of the Terraform Reach that had never been members of the old Alliance, but which the Empire now claimed.
The borders of the Empire have swelled and shrunk several times since then, and the senatorial families have feuded with one another, on and off, producing several different dynasties. The Empire claims systems on several different grounds:
The Empire keeps planets by mere military might, partly, but also by leaving local governments alone, as long as the tribute gets paid and sedition is minimized, and by eliminating war and piracy within its borders. Beyond its borders, neighboring systems often band together in small numbers, to discourage Imperial expansion in their direction.
In keeping with the nomadic, spacefaring culture of the old admirals, the imperial and senatorial families are scattered widely over the Empire. The current imperial seat is on the oneface world Impri, but there are many other imperial residences. Impri is the capital planet, but there is no capital city, and the title "capital planet" has moved repeatedly and randomly among the worlds Impri (originally called "Aksul"), Burran, and Tho.
3100s — Old Settlers enter Reach with early psi-tech
4519 — New Terraformers enter Reach with middle psi-tech
4747 — Koliot Raiders enter Reach with middle psi-tech
4890 — Empire founded
5477 — "now"